In 3GPP (3rd Generation Partnership Project) which is a project aiming to standardize a mobile communication system, the introduction of device-to-device (D2D) communication is discussed as a new function after Release 12 (see Non Patent Literature 1).
In the D2D communication, a plurality of neighboring user terminals perform direct communication without passing through a base station. That is, a data path for the D2D communication does not pass through the base station. On the other hand, a data path for normal communication (cellular communication) in a mobile communication system passes through the base station.